Computer systems are fundamentally comprised of subsystems for storing and retrieving data, manipulating data, and displaying results. Nearly all computer systems today use optical, magnetic or magneto-optical storage media to store and retrieve the bulk of a computer system's data. Successive generations of ever more powerful microprocessors, and increasingly complex software applications that take advantage of these microprocessors, have driven the storage capacity needs of systems higher and have simultaneously driven read and write performance demands higher. Magnetic storage remains one of the few viable technologies for economically storing large amounts of data with acceptable read and write performance.
There are basic components common to nearly all hard disk drives. A hard disk drive typically contains one or more disks clamped to a rotating spindle, heads for reading and writing information to the surfaces of each disk, and an actuator assembly utilizing linear or rotary motion for positioning the head for retrieving information or writing information to a location on the disk. A rotary actuator is a complex assembly that couples the head to a pivot point that allows the head to sweep across the surface of the rotating disk.
The head moves across the surface of the disk writing or reading data to or from concentric tracks on the disk surface. Successive generations of hard disk drives, particularly in laptops and other mobile devices, have scaled to smaller form-factors while simultaneously achieving increases in storage capacity in part by increasing the density of tracks stored on each disk. As track density increases, greater precision is required for movements of the heads. Greater precision in head movements requires improved performance in rotary actuator motion. Improvements in the mechanics of hard disk drives, and in the writing of servo patterns on the disks, have greatly reduced the amount of rotary actuator motion necessary to maintain acceptable track mis-registration (TMR), and seek from head to head on a given cylinder of the hard disk drive. The reduced rotary actuator motion that results from those improvements, however, can negatively impact the low frequency response of the rotary actuator.